U.S. patent number 4,409,006 [Application Number 06/328,033] was granted by the patent office on 1983-10-11 for removal and concentration of organic vapors from gas streams.
Invention is credited to Manlio M. Mattia.
United States Patent |
4,409,006 |
Mattia |
October 11, 1983 |
Removal and concentration of organic vapors from gas streams
Abstract
Organic vapors are removed from a gas stream and concentrated to
a high degree in a continuous adsorption process. The vapor-laden
gas passes through a portion of a cylindrical-shaped adsorber as it
rotates in a plane normal to the gas flow. The rotating adsorber
then moves through several stages including regeneration and
cooling. The vapor-laden gas is spiked with recovered product to
increase the loading on the adsorbent and thus provide a higher
regenerating gas composition. Multi-stage regeneration assures a
high recovery efficiency.
Inventors: |
Mattia; Manlio M. (West
Chester, PA) |
Family
ID: |
23279214 |
Appl.
No.: |
06/328,033 |
Filed: |
December 7, 1981 |
Current U.S.
Class: |
95/113;
95/141 |
Current CPC
Class: |
B01D
53/06 (20130101); B01D 2253/102 (20130101); B01D
2253/106 (20130101); B01D 2253/108 (20130101); B01D
2253/116 (20130101); F24F 2203/1096 (20130101); B01D
2259/40081 (20130101); B01D 2259/4009 (20130101); F24F
2203/1032 (20130101); F24F 2203/1068 (20130101); F24F
2203/1092 (20130101); B01D 2257/70 (20130101) |
Current International
Class: |
B01D
53/06 (20060101); B01D 053/08 () |
Field of
Search: |
;55/28,34,59,60,62,74,75,77,78,181,208,387,389,390 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Spitzer; Robert H.
Attorney, Agent or Firm: Panitch, Schwarze, Jacobs &
Nadel
Claims
I claim:
1. A process for the removal and concentration of organic vapor
from gas streams comprising continuously and simultaneously
conducting various steps on different sections both above and below
a rotating bed of adsorbent material and sequentially rotating the
bed through the steps of:
(a) passing organic vapor-laden gas in a direction normal to said
bed through a first section for adsorption of organic vapors and to
produce a gas stream having a reduced quantity of organic
vapor;
(b) passing a hot, partially inert regenerating gas in a direction
normal to said bed through a second section to substantially
regenerate said adsorbent material and to provide a partially inert
gas stream rich in organic vapor, a portion of which forms a
product stream; and
(c) passing a hot inert gas, substantially free of organic vapor,
in a direction countercurrent to the flow of said organic
vapor-laden gas and normal to said bed through a third section to
provide more complete regeneration of said adsorbent material.
2. The process of claim 1 which further comprises spiking said
organic vapor-laden gas with recovered organic vapor to increase
loading on said adsorbent material and to provide a higher
concentration of organic vapor in the product stream.
3. The process of claim 2 which further comprises cooling and
introducing a slip stream of gas from said second section into said
organic vapor-laden gas which is directed to said first
section.
4. The process of claim 1 which further comprises passing a stream
of cool inert gas in a direction normal to said bed through a
fourth section to cool said adsorbent material.
5. The process of claim 4 wherein said inert cool gas is
continuously cooled in a closed loop.
6. The process of claim 1 wherein said hot regenerating gas is
continuously reheated in a closed loop.
7. The process of claim 6 which further comprises reheating said
hot regenerating gas in a heat exchanger with a slip stream of gas
exiting said second section which has been incinerated to remove
organics.
8. The process of claim 1 wherein said hot inert gas, substantially
free of organic vapor, is derived from a slip stream of gas exiting
said second section which is incinerated to remove organics.
9. The process of claim 1 wherein said adsorbent is activated
carbon.
10. The process of claim 1 wherein said hot inert gas,
substantially free of organic vapor, is derived from an external
source and a portion of the hot, partially inert regenerating gas
which passes through said second section is cooled and directed to
a secondary recovery system.
Description
BACKGROUND OF THE INVENTION
The present invention relates to removal and concentration of
organic vapors from gas streams. More particularly, this invention
concerns economically concentrating and removing organic vapors
from large volumes of gas containing low concentrations of organic
vapors. Furthermore, the present invention can be used at any
pressure and can be applied to both the pollution control and gas
processing industries.
Much of the industrial air pollution that exists today is
attributable to the emission of large volumes of gas contaminated
with organic vapors at very low concentrations. An economical
method of destroying the organic contaminants by incineration has
been described in my U.S. Pat. No. 3,455,089 issued July 15, 1970
entitled "Process For Removing Organic Contaminants From Air".
Also, an economical method of recovering these contaminants has
been described in my U.S. Pat. No. 3,534,529 issued Oct. 20, 1970
entitled "Process For Recovering Organic Vapors From Air Streams".
The two processes described in these patents involve cyclic
operations and therefore could not provide the economy and
flexibility of the continuous process described in my U.S. Pat. No.
4,231,764 issued Nov. 4, 1980 entitled "System For Removing Organic
Contaminants From Air". The process of this patent utilizes a
multi-stage fluid bed adsorption system; one stage for
countercurrent adsorption, two or more stages for regeneration and
one stage for cooling. While this process offered many advantages
over previous processes, it also presented disadvantages which
limited its acceptance in industry. These diadvantages included the
high energy cost to maintain fluidization of the adsorbent, gradual
attrition of the fluidized adsorbent, inability to process varying
flow streams and the limiting vapor velocity required to avoid
entrainment of the adsorbent.
A solvent concentrating system utilizing a rotating adsorbent bed
is described in Bulletin 11B3 of Met-Pro Corporation, Harleysville,
Pa.
Heretofore, it has been most difficult to recover organic
contaminants from gases when they are present in low
concentrations. Known processes require high investment and/or
operating costs. Additionally, the excessive energy requirements
for regeneration make many of these processes prohibitive.
SUMMARY OF THE INVENTION
This invention concerns a process for the removal and concentration
of organic vapor from gas streams. This process involves
continuously and simultaneously conducting various steps on
different sections both above and below a rotating bed of adsorbent
material and sequentially rotating the bed through the steps of:
(1) passing organic vapor-laden gas in a direction normal to the
bed through a first section to absorb organic vapor and to produce
a gas stream having a reduced quantity of organic vapor; (2)
passing a hot, partially inert regenerating gas in a direction
normal to the bed through a second section to substantially
regenerate the adsorbent material and to provide a partially inert
gas stream rich in organic vapor, a portion of which forms a
product stream and (3) passing a hot inert gas, substantially free
of organic vapor in a direction countercurrent to the flow of the
organic vapor-laden gas and normal to the bed through a third
section to provide more complete regeneration of the adsorbent
material thus permitting higher removal efficiency.
In a further embodiment of the process of this invention, the
organic vapor-laden gas is spiked with recovered organic vapor to
increase loading on the adsorbent and provide a higher
concentration of organic vapor in the product stream. Also, in some
process applications of this invention, cooling of the bed may be
required. In cooling the bed of adsorbent material, a stream of
cool inert gas is passed in a direction normal to the bed through a
fourth section.
This invention also concerns an apparatus for the continuous
removal and concentration of organic vapors from gas streams. The
apparatus includes a housing, a axially rotatable bed of adsorbent
material and a plurality of pie-shaped sections separated from each
other by baffles. These sections are disposed both above and below
the bed. The dividers can be movable to vary the cross-sectional
area of the sections. The adsorbent material is disposed in a
plurality of axial channels to substantially prevent lateral flow
of gas.
BRIEF DESCRIPTION OF THE DRAWINGS
For the purpose of illustrating the invention, there are shown in
the drawings forms which are presently preferred; it being
understood, however, that this invention is not limited to the
precise arrangements and instrumentalities shown.
FIG. 1 is a perspective view having a cut-away section depicting an
apparatus for continuous removal and concentration of organic
vapors from gas streams.
FIG. 2 is a sectional view taken along line 2--2 of FIG. 1.
FIG. 3 is a partial perspective view showing in detail the
adsorbent bed of the apparatus shown in FIG. 1.
FIG. 4 is a schematic diagram showing one embodiment of the process
of this invention wherein the concentrated organic vapor recovered
is incinerated.
FIG. 5 is a schematic diagram depicting another embodiment of the
process of this invention wherein concentrated organic vapor is
recovered for reuse.
DETAILED DESCRIPTION OF THE INVENTION
Referring to the drawings, wherein like numerals indicate like
elements, there is shown in FIG. 1 an adsorber apparatus 10 for the
present invention. The cylindrical adsorber bed 12 can be made up
of either granular, fibrous, or a porous solid material and can
contain activated carbon, molecular sieves, silica gel, or other
suitable adsorbent. The adsorbent material is encased in channels
such as containers (cylinders) 14. The containers 14 are fabricated
from any suitable non-permeable material. The cross-sectional size
and shape of each container 14 is important only insofar as it
provides maximum flow normal to the bed 12 without any substantial
corresponding lateral flow through the bed 12. Containers 14 are
packed with adsorbent in a manner which will permit a high gas flow
rate therethrough and provide maximum contact of the flowing gas
with the adsorbent. The containers 14 are packed tightly into the
bed 12 between two perforated plates 16 and 18. The adsorbent
containing containers 14 can be placed in the bed 12 from a single
opening in the adsorber shell 40 while the bed 12 is rotated
manually during the loading operation.
Above and below the bed 12 are plenums 20 and 22 which are divided
into four pie-shaped sections 24, 26, 28 and 30 by baffles 32, 34,
36 and 38 which direct the flow of gas through the bed 12. The
baffles 32, 34, 36 and 38 in plenums 20 and 22 run from the center
of the adsorber 10 radially out to the cylindrical adsorber shell
40. The baffles 32, 34, 36 and 38 are attached to a sleeve 42 in
the center of the adsorber 10 through which a drive shaft (not
shown) rotates. The baffles 32, 34, 36 and 38 fit tightly between
the sleeve 42 and the adsorber shell 40. A radial seal 44 (see FIG.
3) is attached to each baffle 32, 34, 36 and 38 both above and
below the bed 12 so as to prevent the flow of gas from one section
to another. The seal 44 may be constructed of any suitable
elastomeric material which will withstand the operating conditions
in the adsorber 10. In applications involving high temperatures not
suitable for elastomeric materials, the seal 44 could be fabricated
from metallic materials. Such elastomers provide a better seal than
metals. Accordingly, in lower temperature processes an elastomer
seal is preferred. The seal 44 rides on the perforated plates 16
and 18 as the adsorber bed 12 slowly rotates.
The perforations in plates 16 and 18 communicate with the
pie-shaped sections 24, 26, 28 and 30 and the containers 14 to
allow gas to flow in a normal direction through the bed 12. It is
anticipated that there will be numerous perforations per container
14. In some instances, it may be preferred that the containers 14
align with perforations in plates 16 and 18.
A circumferential seal 46 (see FIG. 2) is attached to the adsorber
shell along the entire circumference of the adsorber 10 both below
and above the bed 12. This seal 46 is in contact with the
perforated plates 16 and 18 as the bed 12 rotates. The
circumferential seal 46 prevents gas from by-passing the adsorber
bed 12. Like seal 44, the circumferencial seal 46 can be fabricated
from a suitable elastomeric or metallic material depending on the
processing conditions.
Special adjustments may be required where the radial baffle seal 44
meets the circumferential seal 46 in order to prevent gas leakage
between the sections 24, 26, 28 and 30. A suitable design could be
to slit the radial seal 44 at the junction of the circumferential
seal 46 so that it rides firmly on the perforated plates 16 and 18
at this point.
FIG. 4 is a schematic flow sheet of the process of this invention
depicting the flow scheme when the concentrated organic vapors are
to be incinerated so as to provide the heat and inert gas required
for the regenerating systems.
In FIG. 4, the adsorber 10 is represented in schematic form.
Partitioned sections above and below the rotating bed are dedicated
specifically for adsorption, regeneration, hot gas sweep and
cooling. These sections correspond respectively to pie-shaped
sections 24, 26, 38 and 30 shown in FIG. 1.
A major portion of the bed 12 is the adsorption section 24 which is
allocated for adsorbing organic vapor from organic vapor-laden gas
streams. Another zone 26 is dedicated to hot gas regeneration. The
next zone 28 is a hot, clean gas sweep which provides for more
complete regeneration of the adsorbent material. Finally, in a gas
cooling zone 30, the bed is cooled and prepared for adsorption.
Organic vapor-laden gas, such as air, enters the adsorber 10
through line 48, into the top of the first sub-plenum 50 in top
plenum 20 through an inlet (not shown) and then flows vertically
down through the adsorber bed 12 and into the bottom of the first
sub-plenum 52. Organic vapors are removed from the gas by the
adsorbent and relatively organic vapor free gas leaves sub-plenum
52 through an outlet (not shown) and then through conduit 54. This
gas may be either discharged to the atmosphere or returned for
further processing.
The adsorber bed 12 rotates continuously at a slow rate while
plenums 20 and 24 containing the pie-shaped sections 24, 26, 28 and
30 remain stationary. The organic loaded adsorbent moves from the
adsorption section 24 into the first regeneration zone 26 where the
organic vapor is stripped from the adsorbent by hot, inert
regenerating gas.
Hot, partially inert regenerating gas enters the bottom of the
second sub-plenum 56 through conduit 58 and an inlet (not shown).
The hot regenerating gas moves vertically up through the adsorber
bed 12 into the top of the second sub-plenum 60 and then leaves
through an outlet (not shown) and line 62. The hot regenerating gas
containing stripped organic vapors flows to the hot gas
regenerating blower 64 which discharges into line 66. The hot
regenerating gas in line 68 flows through heat exchanger 70 where
it is heated to provide the required temperature for regenerating
the adsorbent. The hot regenerating gas then flows through line 58
back into the hot gas regenerating sub-plenum (bottom second
sub-plenum) 56 through an inlet (not shown).
A slip stream is withdrawn from the hot regenerating gas loop
through lines 72 and 74 respectively. Gas in line 74 flows into an
incinerator 76. The high organic content in this gas stream
provides the fuel for incineration. In the incinerator 76, the
organic vapors are destroyed at elevated temperatures. Combustion
air is provided by air blower 78 which is fed to incinerator 76
through line 80. The incinerator 76 provides the requisite heat and
inert gas for regeneration of the adsorbent material as described
in my U.S. Pat. No. 3,455,089.
Flow of combustion air to the incinerator 76 is controlled to
maintain a low oxygen content in the flue gas which leaves
incinerator through line 82 to produce a substantially inert gas.
As used throughout the specification and claims herein, "inert gas"
refers to gas having a low oxygen and carbon monoxide gas content.
The use of inert gas in the process of this invention serves to
reduce the incidence of hazardous conditions such as fires and
explosions.
The hot flue gas flows to heat exchanger 70 where it heats the
regenerating gas from line 68. The incinerator flue gas then flows
through line 84 and enters the bottom of the third sub-plenum 86.
The flow of hot incinerator flue gas, substantially inert, is
controlled by valve 88 so as to provide the minimum flow necessary
to remove residual organic vapors remaining in the partially
regenerated adsorbent.
The organic vapor free incinerator flue gas (not sweep gas)
provides a low partial pressure of organic vapor over the adsorbent
so as to obtain a highly regenerated adsorbent. The hot sweep flows
from sub-plenum 86 up through adsorber bed 12 and into the top of
the third sub-plenum 90. This hot sweep gas now rich in organic
vapor leaves sub-plenum 90 through an outlet (not shown) and then
through line 92 where it combines with the hot regenerating gas in
line 62. Excess flue gas not required for the hot gas sweep is
discharged to the atmosphere through line 94.
Another slip stream leaves the hot gas regenerating system through
line 72 and flows to cooler 96 where it is cooled to the
temperature of the organic vapor-laden gas stream entering through
line 48. The cooled regenerating gas, rich in organic vapor, is
added to the organic vapor-laden feed stream through line 98. Valve
100 controls the flow of the cooled regenerating gas. Adding gas
rich in organic vapors to the feed stream in line 48 provides a
higher concentration of organic vapor contacting the adsorbent.
Consequently, the organic vapor loading on the adsorbent is greatly
increased. When this more highly loaded adsorbent is regenerated, a
correspondingly higher organic vapor concentration is obtained in
the regenerating gas. Since the adsorbent has been thoroughly
regenerated, the higher organic vapor content in the feed gas can
be removed at a very high efficiency level.
After the adsorbent has been swept with hot flue gas and a high
degree of regeneration has been accomplished, the adsorber bed 12
rotates into the cooling zone. Cool inert gas from line 102 enters
the bottom of the fourth sub-plenum 104 through an inlet (not
shown) and flows up through the adsorber bed 12 into the top of the
fourth sub-plenum 106. The cooling gas leaves through an outlet
(not shown) and through line 108 where it flows to the cooling
recirculation blower 110. The cooling gas then flows through line
112 through cooler 114 and re-enters the bottom of the fourth
sub-plenum 104 through line 102 into an inlet (not shown).
The flue gas which enters the hot sweep section provides gas for
the entire regeneration and cooling section. This is accomplished
because hot sweep gas leaving the adsorber through line 92 is added
to the regenerating system at line 62 thus maintaining a high level
of inert gas in this system. Also, residual flue gas retained in
the void spaces surrounding the adsorbent is carried to the cooling
zone as the adsorber bed 12 rotates into that section. This action
maintains a high level of inert gas in the cooling section.
The direction of flow of the cooling gas and the hot regenerating
gas can either be co-current or counter-current relative to the
flow of the organic vapor-laden feed gas. The hot gas sweep,
however, is to flow counter-current relative to the flow of the
organic vapor-laden feed gas in order to insure substantially
complete regeneration of the adsorbent material.
In some process applications, cooling of the adsorbent material
after the hot gas sweep would not be required. Accordingly, the
entire cooling system would not be necessary.
FIG. 5 is a schematic flow sheet of the process which is employed
when the concentrated organic vapors are to be recovered. The
adsorption and cooling systems for this process are identical to
the systems described in FIG. 4 with only minor differences
existing in the regeneration and the hot sweep systems.
Hot regenerating gas flows into the bottom of the second sub-plenum
56 and up through adsorber 12 where it strips organic vapor from
the adsorbent. The rich, hot regenerating gas flows into the top of
the second sub-plenum 60 and leaves the adsorber through line 62.
The hot gas regenerating blower 64 forces the gas through line 68
to the regenerating gas heater 116 where the regenerating gas is
heated by steam or some other external source of heat. The hot
regenerating gas then flows through line 58 back into sub-plenum
56.
A slip stream leaves the regenerating system through line 72 where
the organic rich regenerating gas is cooled in cooler 96 to a
temperature generally below about 100.degree. F. The temperatures
of the cooling gas and regeneration gas are dependent on the nature
of the adsorbent, the nature of the organic vapors removed and the
desired degree of removal of organic vapors. The cooled gas flows
through line 98. A controlled amount of this gas, as controlled by
valve 118, flows through conduit 98 where it is added to the
organic vapor-laden gas feed stream in line 48. The remainder of
the gas is the recovered product which leaves the system through
line 120. This highly concentrated organic vapor can be directed to
a secondary recovery system 122 which could be, for example, a
condensing tower as described in U.S. Pat. No. 4,231,764 or a small
adsorber as described in U.S. Pat. No. 3,534,529. Any organic vapor
not recovered in the secondary recovery system 122 can be returned
to line 98 via conduit 124 and constitute the organic vapor stream
which enriches the feed gas stream in line 48.
An outside source of inert gas enters the hot sweep system through
line 126. The gas is heated to approximately 250.degree. F. in the
inert gas heater 129 and then flows through line 130 into the hot
sweep sub-plenum 86. The hot sweep gas flows up through the
adsorber into sub-plenum 90 and then continues to follow the flow
pattern as described in FIG. 4.
A system of the present invention required to treat 20,000 CFM of
air containing 200 ppm of toluene may be designed to the following
specifications. An adsorber 13 feet in diameter would be
partitioned so as to provide 70% of the cross-sectional flow area
for adsorption and 10% each for regeneration, hot gas sweep and
cooling. The adsorbent may be activated carbon packed to a depth of
2 feet. The adsorber would rotate once every four hours. Thus, each
section of adsorbent will remain in the adsorption zone for three
hours and in each of the other zones for 20 minutes. The following
approximate face velocities are anticipated for each zone:
Adsorption: 200 Ft./Min.
Regeneration: 150 Ft./Min.
Hot Gas Sweep: 40 Ft./Min.
Cooling: 150 Ft./Min.
The working load on the adsorbent is conservatively estimated to be
10 lbs. of solvent to 100 lbs. of adsorbent. The regeneration and
hot sweep gas temperature should be at approximately 300.degree. F.
Sufficient cooled regenerating gas is recycled to the organic
vapor-laden air feed stream so as to increase the solvent
concentration from about 200 ppm to about 500 ppm. Based on
standard isotherms for toluene on granular activated carbon, the
product gas flow should amount to only about 300 CFM of gas
containing 1.4% toluene. This represents a 70 fold reduction in gas
flow and a corresponding increase in solvent concentration.
The flow sheets described in FIGS. 4 and 5 can be modified so as to
provide both solvent recovery and incineration. A portion of the
product stream would then be incinerated to provide the heat and
inert gas required for the regeneration and cooling systems.
The present invention provides the following advantageous
features:
(1) an efficient and economical system for recovering organic
vapors from gas streams and concentrating them to a much higher
level;
(2) a novel system for removing organic vapors in a safe and
continuous manner;
(3) a novel regenerating system which assures more complete
regeneration of the adsorbent and thereby permits a higher removal
efficiency;
(4) ability to obtain a 50 to 100 fold increase in vapor
concentration with a corresponding reduction in volumetric gas
flow.
The present invention may be embodied in other specific forms
without departing from the spirit or essential attributes thereof
and, accordingly, reference should be made to the appended claims,
rather than to the foregoing specification, as indicating the scope
of the invention.
* * * * *